I've used Daniel at Tanisha Tours, and I've been to Tikal (but not with Daniel -- via a driver hired through Katie Valk, who is also wonderful!).
I cannot say enough good things about Daniel. He gives you a quality experience because he honestly, deeply cares about the animals and birds you see on his trips, and because he cares, he's very knowledgable about them. And he spends a lot of time explaining things -- you can tell, it's not just about getting the tour over with for him. Also, the food he provided at Lamanai was so delicious, I'm still thinking about it a year later! If there were ever a choice, I would definitely go with Tanisha Tours. He was good to my mother and her friend, too, when they had trouble with the hiking, and took the time to take care of us during our two tours with Tanisha. We felt safe with Daniel, and he was excellent company, too.
Regarding Tikal...YOU MUST GO! I've been there twice because the first time was not nearly enough. It's got to be one of the most magical places on earth. Also, if you want to see animals like foxes, howler monkeys, and coatis, this is the greatest place because they have no fear of people at all. Unless you hate history, you'd be crazy to pass up a chance to see Tikal -- it's absolutely breath-taking.